Ferulic acid Added (ng/ml) Stability Mean (ng/ml) SD RSD (%) RE (%) 5 5.46 0.27 4.9 9.1 500 565.09 4.10 0.7 13.0 3000 2789.91 41.77 1.5 -7.0

Ferulic acid standard solution at different concentrations of 5, 500 and 3,000 ng/ml in rat plasma was prepared. After storage for 30 days at -20°C, the samples were injected into UPLC-MS/MS to determine the stability of ferulic acid. Mean of the concentration (ng/ml) of ferulic acid in rat plasma, SD, RSD (%) and RE (%) was calculated, n = 3.

Table 7: Stability for the anaylsis of ferulic acid after storage at -20°C for 30 days